Electrical conductivity and magnetic dynamos in magma oceans of Super-Earths

François Soubiran (1) , Burkhard Militzer

1 LGL-TPE - Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement

Super-Earths are extremely common among the numerous exoplanets that have been discovered. The high pressures and temperatures in their interiors are likely to lead to long-lived magma oceans. If their electrical conductivity is sufficiently high, the mantles of Super-Earth would generate their own magnetic fields. With ab initio simulations, we show that upon melting, the behavior of typical mantle silicates changes from semi-conducting to semi-metallic. The electrical conductivity increases and the optical properties are substantially modified. Melting could thus be detected with high-precision reflectivity measurements during the short time scales of shock experiments. We estimate the electrical conductivity of mantle silicates to be of the order of 100 Omega(-1) cm(-1), which implies that a magnetic dynamo process would develop in the magma oceans of Super-Earths if their convective velocities have typical values of 1 mm/s or higher. We predict exoplanets with rotation periods longer than 2 days to have multipolar magnetic fields.

Domaines: Planète et Univers [physics]

François Soubiran, Burkhard Militzer. Electrical conductivity and magnetic dynamos in magma oceans of Super-Earths. Nature Communications, 2018, 9, ⟨10.1038/s41467-018-06432-6⟩. ⟨hal-02327161⟩